Compute tooltip text lazily?

[mootari]

I have a plot that gets rerendered very frequently. The plot includes a custom tooltip text that is fairly expensive to calculate. Although the tooltip won't be viewed most of the time, the title reducer still gets invoked for every single group on every render.

What would be the recommended way to calculate the title value only for the index that is about to be shown?

[Fil]

I'd use a render function. See for example https://observablehq.com/d/716cfebafbd2683a